An object is placed at a distance of 20 cm in front of a concave mirror of focal length 10 cm. Determine the position of the image. What is the ratio of the size of the image to the size of the object ?

Explanation

Here, u = - 20 cm, f = - 10 cm
According to the equation of spherical mirror,
`(1)/(v) + (1)/(u) = (1)/(f)`
`or, " " (1)/(v) + (1)/(-20) = - (1)/(10)`
`or, " " (1)/(v) = (1)/(20) -(1)/(10) = (1-2)/(20) = - (1)/(20)`
`or, " " v = - 20 cm`
`therefore` The image will be formed in front of the concave mirror at a distance of 20 cm.
`Now " " ("Size of the image" (I))/("Size of the object"(O))= -(v)/(u) = - (-20)/(-20) = - 1`
The negative signs shows that the image is real. Hence the ration of the of the image of the size of the object is 1 : 1 .